The present work constitutes a beginning step in identifying the psychobiological origins of the Type A behavior pattern, an established risk factor for coronary heart disease. Overt behavioral manifestations of Type A are extremes of competitive achievement-striving, a sense of time urgency and impatience, and an aggressive hostility. Individuals thought to exhibit those behaviors are called Type As, whereas those who do not are called Type Bs. Based on evidence from longitudinal studies of personality development, it was decided that childhood and adolescence are likely to be the periods when the overt characteristics of Type A emerge and stabilize. In order to study the origins of Type A in the developing individual, a way of measuring Type A behaviors was needed. A set of rating scales, called the MYTH, was designed to identify children who are rated by their classroom teachers as exhibiting competitive achievement-striving, impatience, and aggression-hostility. The MYTH is reliable across time and can predict children's impatience and aggression. The current research was designed to complete the basic psychometric studies on the MYTH. Studies are being conducted to: (a) obtain an estimate of the MYTH's reliability; (b) examine the MYTH's validity as a measure of children's achievement-striving; and (c) investigate the hemodynamic responses during a challenging task of fifth grade children who score high and low on the MYTH. The last investigation was included because Type A adults as young as 18 years old show elevations in systolic blood pressure while performing a challenging task and thus, the present study can test for Type A adult-child similarities in hemodynamic responses.